1. Field of the Invention
The present invention relates to a hinge device for coupling a unit such as a document press unit or a document feeder used for an image forming apparatus such as a copying machine, an image scanner, or a printer to an image processing unit so that the unit can be freely opened or closed, and more particularly to a hinge device which performs readjustment of a vertical load of the unit by means of friction.
2. Related Background Art
Conventionally, there is a unit for screening light streaming paths to an image forming apparatus and for conveying a document with applying an appropriate pressure to the document against a platen. If the unit is coupled to the image forming apparatus such as a copying machine so that it can be opened or closed freely, a hinge device is used to couple a side of the image forming apparatus in a document conveying direction to an opposite side of the unit for the open-close action.
This hinge device has a first fixing member fixed to the image forming apparatus and a second fixing member fixed to the unit being connected to each other by means of a rotating shaft so as to be free to take rotational movements, with an expansible cushioning member such as a spring or a hydraulic cylinder put between the first and second fixing members, so as to reduce or adjust a weight for opening or closing the unit by means of the cushioning member.
In conventional hinge devices, from the viewpoint of a fixing relationship between the first and second fixing members and the cushioning member, there are known two types of hinge devices; one is a hinge device (a) having a cushioning member whose both ends are supported by the first and second fixing members so as to be free to take rotational movements and the other is a hinge device (b) having a configuration in which a spring action of a cushioning member is used to apply a contact pressure to one end of a cam surface arranged on one of the first and second fixing members for opening or closing the fixing members so as to be along the cam surface.
Although the hinge device (a) has a simple configuration in which the opening or closing action is controlled only by force of a spring or a hydraulic cylinder, its operating force of the open-close action cannot be arbitrarily set. On the other hand, although the hinge device (b) allows its operating force of the open-close action to be set as designed since the open-close action is controlled by the cam surface in addition to the force of the spring, it has a complicated configuration. In addition, in both types of the conventional hinge devices (a) and (b), in some cases, there occurs unevenness of a weight for opening or closing on the unit to be opened or closed, or a sudden or slow open-close action occurs if an uneven force is required for the operation according to an open-close position, which leads to a dangerous condition or by which an appropriate pressure cannot be applied to a platen. To cope with this problem, a friction member is arranged for a readjustment of a vertical load at opening or closing separately from the cushioning member, so as to prevent such a sudden action.
As a configuration of the friction member for this readjustment, a cylinder member and a piston member are installed with engaging with one and the other of the fixing members, so as to be used to readjust the open-close action or to relieve an interlocking action by means of a frictional resistance of sliding when the cylinder member and the piston member are sliding together with the open-close action of the unit. This configuration, however, has a disadvantage that an initial frictional force cannot be applied due to wearing of the cylinder member and the piston member caused by use or a temperature change during use.
Principally it is an object of the present invention to provide a hinge device which allows a smooth open-close action by damping an action of a cushioning member at the open-close action in a simple configuration, and it is another object of the present invention to provide a hinge device which allows its controlling force to be increased or decreased according to an open-close angle.
To achieve these objects, there is provided a hinge device according to the present invention comprising first and second fixing members connected to each other by means of a rotating shaft so that they can take relative rotational movements and a cushioning member which is expandable and rocking in response to the rotational movements of the fixing members with one end supported by the first fixing member and the other end supported by the second fixing member,
wherein there are provided a rotating member which is connected to at least one end of the above cushioning member so as to rock or rotate in response to the rocking motion of the cushioning member and a friction member which is put into contact with the rocking member or the rotating member so as to damp the rocking motion of the cushioning member.